Liquid crystal display

Abstract

A liquid crystal display is provided and includes: a liquid crystal panel; light sources for illuminate light from M kinds of colors onto the liquid crystal panel; and a light source driving unit in which a one-frame period of an input image signal is divided into M or more subfields, and the light sources are sequentially driven in a time-sharing mode in correspondence with the subfields. The light source driving unit changes in correspondence with the input image signal at least one of an emission intensity and an emission period of a light source in a period of the subfield and the number of emission times of the light source during the one-frame period. Alternatively, a liquid crystal driving unit performs gradation control for changing a gradation characteristic independently with respect to each of the light sources, the gradation characteristic representing a relationship of emission intensity of each of the light sources with respect to the input image signal. The maximum luminance of a specific color in the subfield is thereby changed.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a liquid crystal display, and more particularly to a technique for improving color reproducibility and dynamic contrast.[0003]2. Description of Related Art[0004]Cathode ray tubes (CRTs) have hitherto been mainly used as displays employed in office automation (OA) equipment such as word processors, laptop computers, and monitors for personal computers, portable terminals, televisions, and the like. In recent years, however, liquid crystal displays have come to be used widely instead of the CRTs.[0005]The displays using liquid crystal display devices (also called liquid crystal display panels) are capable of displaying images without providing a space (vacuum housing) for the two-dimensional scanning of an electron beam on the rear side of a display screen as in the cathode ray tube (CRT). Accordingly, these displays have characteristics of being thinner, more lightweight, and lower in pow...

AI Technical Summary

Benefits of technology

[0144]Each of the optically anisotropic layers 31A and 31B is disposed between the respective one of the protective films 33A and 33B and the liquid crystal cell. The optically anisotropic layers 31A and 31B are layers which are formed of a composition containing a liquid crystalline compound, e.g., a rod-like compound or a discotic compound. In the optically anisotropic layer, the molecules of the liquid crystalline compound are fixed in a predetermined alignment state. The slow axes 5 and 11 in the planes of the protective films 33A and 33B, on the one hand, and average directions of orientation, RD1 and RD4, at least at the interfaces on the sides of the protective films 33A and 33B, of molecular symmetrical axes of the liquid crystalline compounds in the optically anisotropic layers 31A and 31B, on the other hand, intersect each other at approximately 45 degrees. If the optically anisotropic layers 31A and 31B and the protective films 33A and 33B are disposed in the above-described relationship, the optically anisotropic layers 31A and 31b produce retardations with respect to the incident light from the normal direction, so that light leakage is not generated, and the effect of the invention can be sufficiently demonstrated with respect to the incident light from diagonal directions. At the interface on the liquid crystal cell side as well, the average directions of orientation of the molecular symmetrical axes of the optically anisotropic layers 31A and 31B are preferably at approximately 45 degrees to the slow axes 5 and 11 in the planes of the protective films 33A and 33B.

[0145]Here, a more detailed description will be given of the liquid crystal display shown in FIG. 10.

[0146]In this liquid crystal display, the bent alignment liquid crystal cell (10) is optically compensated through cooperation between optically anisotropic layers (31A, 31B) formed from a discotic compound and transparent supports (33A, 33B) having optical anisotropy.

[0147]If the rubbing directions (RD1, RD4) for aligning the discotic compound in the optically anisotropic layers (31A, 31B) are set in an anti-parallel relation to the rubbing directions (7, 9) of the liquid crystal cell, the liquid crystal molecules of the bend alignment liquid crystal (10) and the discotic compound of the optically anisotropic layers (31A, 31B) correspond and optically compensate. Further, it has been so designed that the optical anisotropy of the transparent supports (33A, 33B) corresponds to the liquid crystal molecules which are substantially vertically oriented in the central portion of the bend alignment liquid crystal (10). It should be noted that ellipses depicted in the liquid crystal cell are refractive index ellipses which are generated due to the optical anisotropy of the transparent supports. Thus, as optical characteristics of the optically anisotropic layers and transparent supports of optical compensatory sheets are adjusted in correspondence with the orientation of the liquid crystal in the black display state of the liquid crystal cell, the optical anisotropy of the liquid crystal cell can be compensated to a high degree, and a wide viewing angle can be realized.

[0148]The rubbing direction (7, 9) of the liquid crystal cell may be an arbitrary direction in the plane of the screen, but should preferably be a lateral direction, a lengthwise direction, a 45-degree direction, or a 135-degree direction in the plane of the screen.

[0149]If two polarizing films are arranged in a crossed Nicols configuration, the transmittance as viewed from direction normal to the polarizing film is very low, but if the viewing angle is tilted from the normal direction toward the direction of a median line between the transmission axes of the two polarizing films, the transmittance become large. This is because, as described in SID '98 Digest, p. 315, the tilting of the viewing angle causes the angle formed by the transmission axes of the incident-side polarizing film and the emission-side polarizing film to be offset from the crossed Nicols configuration (90°). The light leakage at the time when this viewing angle is tilted can be substantially reduced by a combination of a positive A-plate and a positive C-plate, a combination of a negative A-plate and a negative C-plate, or the use of a biaxial film. Here, in the case of the combination of the A-plate and the C-plate, the optical axis of the A-plate is disposed parallel to the transmission axis of the polarizing film, and in the case of the biaxial film, the slow axis is disposed parallel to the transmission axis of the polarizing film.

Problems solved by technology

However, in order to display images comparable to those of CRTs, the implementation of a higher luminance and the improvement of a reproducible color gamut have also become important issues.

Because of this, it has been regarded as difficult for the liquid crystal displays to implement complete moving picture display.

However, since the color filters effect color display through the absorption of light, their light transmittances are low, so that their efficiency of use as display lights has been low.

Further, the color filters are expensive among the costs of members of the color liquid crystal display panel, and it is possible to attain a substantial reduction in cost by eliminating the color filters.

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